In order to assess the prospects for and appropriate design of remedial works to protect the embankments at Fort Anne National Historic Site from continuing erosion, a research programme to examine hydrodynamic and sedimentological processes in neighbouring portions of the Annapolis Basin and Estuary was conducted from 12 to 18 June 1994. The project was a cooperative exercise involving three research groups: the Acadia Centre for Estuarine Research, the Atlantic Geoscience Centre (Bedford Institute of Oceanography), and the Institute for Marine Dynamics (National Research Council of Canada, Ottawa). The combined intellectual and material resources of these three groups was essential to the success of the project. Each group also provided 'in-kind' resources in order to enable the project to be completed.

Recording current meters were deployed at three locations in the central axis of the estuary, and at three other locations on the Fort Anne foreshore, to provide data for construction and calibration of a hydrodynamic model. These data were forwarded to the Institute for Marine Dynamics for modelling purposes.

Geotechnical investigations were conducted by the Atlantic Geoscience Centre. Four soil cores were obtained using a portable gravity percussion sampler. Observations during coring indicated that the embankment of the southwest ravelin consists of marine clays with interbedded saltmarsh roots. A small landslip occurred on the seaward face of this slope in March 1994. The laminations exposed by the slip indicate that the embankment is a natural deposit, representing a local topographic high. Vertical standpipes have been installed at the four coring sites along the slope to assist with detection of further movements, and with identification of any internal slip surface. These piezometer pipes are suitable for the monitoring of groundwater levels in the embankment.

Granulometric tests of cores indicate that the 'red mud' that overlies the glacial till is a silty clay (56% silt, 44% clay) of post-glacial origin. Shear tests confirm previous observations that it is overconsolidated, and has a plasticity index of 29% (liquid limit 55%; plastic limit 26%). Undrained shear strength of undisturbed core subsamples ranged from 180 to 690 kPa.

As a result of observations made during the early field study, plans to reinstate the rockfill berm at the toe of the slope were advanced, and the work was completed by Parks personnel during the summer. Calculations of slope stability indicate that without the rock fill that had eroded away, the slope was unstable; emplacement of approximately 1000 tonnes of rock has reestablished stability for the near future, however, further remediation is required. It is also recommended that water levels in the standpipes be monitored regularly for assessment of the groundwater table.

A series of seven deployments of 'Sea Carousel', a field-deployable annular flume, was made along the axis of the Annapolis Estuary to examine the in situ shear strength and erodibility of the bottom sediments. The field study was a cooperative effort of the Acadia Centre for Estuarine Research and the Atlantic Geoscience Centre. Field measurements were made of water column salinity, temperature and suspended solid concentrations at each 'Sea Carousel' site. Grab samples were taken for analysis of sediment and biological characteristics.

Difficulties were experienced in maintaining position during the two-hour long deployments at stations nearest Digby because of strong winds. Nonetheless, complete deployments were successfully made in the Estuary (the region between the Annapolis Causeway and Goat Island), the area of greatest significance for modelling purposes. Results of 'Sea Carousel' deployments showed that the sediment surface in the inner Annapolis Basin in the vicinity of Fort Anne is highly erodible, exhibiting erosion at critical shear stresses of 0.3 to 0.6 Pa. The results are conformable with those of remolded sediments examined in laboratory flumes at the Acadia Centre for Estuarine Research and the Canada Centre for Inland Waters.

Analyses of grab and core samples at each of the anchor stations indicates that the abundance and diversity of benthic organisms is greater at stations in the Basin than in the Estuary. Although polychaete worms are numerically dominant throughout, a greater variety of polychaetes and crustaceans is present in the coarser sediments characteristic of the Basin. In the Estuary, the finer sediments are actively disturbed (bioturbated) by burrowing invertebrates. Chlorophyll and carbohydrate concentrations in sediments of the Estuary suggest that biological production is lower in the Estuary than the Basin, although in some respects the station nearest to Fort Anne appears anomalously high. The intertidal fauna at Fort Anne is poorly developed, reflecting the instability of the surface. The burrowing amphipod Corophium volutator, is numerically dominant, and its activities may increase susceptibility of the surface sediment to resuspension. Remedial action to transform the intertidal mudflat at Fort Anne into a rocky shore might increase benthic production as well as minimise further erosion.

Recommendations arising from the study include:
(1) That discussions regarding engineering solutions for protection of the embankment and saltmarsh against erosion be initiated immediately.
(2) That a multidisciplinary team be established to develop and select appropriate engineering solutions.
(3) That solutions considered should address two problems : erosion of the Fort embankment and residual marsh at the high water level; erosion of exposed intertidal silty-clay by tidal resuspension. Possible solutions to be considered should include : rebuilding of Queen's Wharf; reconstruction of the groyne (i.e., the "Scottish"? wharf) at the junction of Allain River and the Annapolis Estuary; rockfill protection of remnant saltmarshes; covering of exposed intertidal sediments by a more erosion-resistant material.
(4) That water table levels in the embankment be monitored regularly.
(5) That the position of rocks laid down as part of recent remedial work should be monitored in order to detect continued movement.
(6) That a mid-summer survey of benthic intertidal fauna be conducted.
(7) That experiments be designed and conducted to examine the feasibility of sealing the exposed intertidal sediment to prevent its further loss.